Such devices may be used for switching in and out any type of load with respect to an alternating voltage feeder, especially a three-phase alternating voltage feeder, such as an electricity network for distribution or transmission of electric power. However, the invention is directed to such feeders having at least one phase and not only three-phases, although that may be the most common use thereof. Thus, the load may for instance be a capacitor bank used for reactive power compensation and switched in dependence of conditions prevailing at such a network, such as the consumption of for instance an industry connected thereto for reducing losses. The use of a switching device of this type for switching in and out a load comprising one or more capacitors will hereinafter be discussed for illuminating the invention but not in any way restrict the invention to that application.
It is known to use so called vacuum contactors for switching in and out capacitors with respect to a three-phase alternating voltage feeder for reactive power compensation. However, switching with such vacuum contactors is neither synchronized with the current nor the voltage in said feeder or network, which may result in inrush currents at closing the current path between said two main contacts (switching in) and re-strikes at opening (switching out). Thus, it is necessary to install reactors in series with the capacitor or capacitor bank to limit the current transients, which may be harmful to equipment connected to the network.